The present invention relates to an electronic fuel injection apparatus and especially a digital control fuel injection apparatus in which the opening time duration of a fuel injection valve is dependent upon a stored data output from a memory in response to an engine driving condition.
In an internal combustion engine, for reducing the pollution of exhaust gases from the engine and for improving the efficiency of the engine operation, it is necessary to precisely adjust the fuel quantity supplied to the engine. The fuel quantity may be determined as a function of two parameters, such as engine speed and throttle opening or intake suction, representing an engine driving condition, and is continuously changed by continuously changing these two parameters. Namely, the fuel injection quantity may be represented by mathematical surface produced by these two parameters. It is impossible to store such a mathematical surface. Therefore, these parameters are respectively divided into a large number of segments, in a rectangular coordinate system and each small surface defined by one segment of a first parameter X and one segment of a second parameter Y has only one value along the Z axis.
In a conventional system, if the first parameter X is an m bit, digital signal and the second parameter Y is a 1 bit digital signal, the number of memorized addresses is 2 .sup.(m.sup.+1). Namely, each memorized address corresponds to each small surface, so that the number of memorized addresses becomes large. For reducing the number of addresses, the divisional numbers corresponding to the first and second parameters X and Y are decreased. However, the control accuracy for the fuel control system becomes significantly reduced, and an interpolation circuit is required for increasing the degree of control accuracy. Therefore, the apparatus is expensive to manufacture.